Recycled utilization of ryegrass litter in constructed wetland coupled microbial fuel cell for carbon-limited wastewater treatment

To solve wetland plant litter disposal and improve the nitrogen removal of carbon-limited wastewater, the integration of microbial fuel cell (MFC) and recycled utilization of ryegrass litter planted in constructed wetland (CW) may be effective. CW and MFC-CW with periodical ryegrass litter addition (10 days one cycle) were constructed to study the effects of ryegrass litter on nitrogen removal, electricity production and microorganism community. The results showed that total nitrogen removal of CW and MFC-CW after ryegrass litter addition reached 80.54 +/- 10.99% and 81.94 +/- 7.30%, increased by 22.19% and 17.50%, respectively. Three-dimensional excitation emission matrix fluorescence spectroscopy results revealed that the soluble organic matters produced by the hydrolyzed ryegrass litter were mainly tryptophan, tyrosine and fulvic acid, which promoted the growth of microorganisms and denitrification. The dosage of 200 g m(-2) did not cause the rise of refractory organic matter in the effluent. The ryegrass litter addition promoted the average voltage and power density slightly in MFC-CW, but the internal resistance also increased temporarily. Compared to the sole CW, current stimulation caused by MFC not only helped to increase the denitrification, but also accelerated the biomass hydrolysis. MFC could contribute to the enrichment and growth of functional microorganisms related to denitrification and organic degradation, such as Vogesella, Devosia, Thermomonas and Brevibacterium. The bacterial genera involved in the ryegrass litter degradation were mainly Thermomonas, Propionicimonas, TM7a, Clostridium_sensu_stricto_1 and so on. This study provided a promising way for practical applications of MFC-CW in the treatment of carbon-limited wastewater, especially in small ecological facilities.

Automated summary

The integration of microbial fuel cell (MFC) and recycled utilization of ryegrass litter planted in constructed wetland (CW) can effectively solve wetland plant litter disposal and improve the nitrogen removal of carbon-limited wastewater. The addition of ryegrass litter significantly increased the nitrogen removal rate and promoted microbial growth and denitrification. In MFC-CW, the introduction of MFC not only increased denitrification, but also accelerated biomass hydrolysis and promoted the enrichment and growth of functional microorganisms.